Darifenacin is an active pharmaceutical substance indicated for the treatment of overactive bladder with symptoms of urge urinary incontinence, urgency, and frequency. Darifenacin is the international common accepted name for (S)-2-{1-[2-(2,3-dihydrobenzofuran-5-yl)ethyl]-3-pyrrolidinyl}-2,2-diphenylacetamide hydrobromide, having an empirical formula of C28H30N2O2.HBr and the structure below.

Darifenacin and its pharmaceutically acceptable salts are reported in U.S. Pat. No. 5,096,890 (the '890 patent). In this reference, different routes for the preparation of darifenacin and pharmaceutically acceptable salts thereof are described. Scheme 1 summarizes the synthetic processes disclosed in the '890 patent.

A specific example for the preparation of darifenacin according to one of the synthetic routes shown in Scheme 1 and included in the '890 patent is detailed in Scheme 2.

Using the processes described in the '890 patent, darifenacin is obtained in low yields and with low purity. In addition, some operations described in the '890 patent are not suitable for industrial scale up, such as, for example, purification by column chromatography.
No improved synthetic processes have been found in the literature for the preparation of darifenacin. Thus, there is a need to develop a process for preparing darifenacin and/or one of its pharmaceutically acceptable salts in a simplified way and yielding higher purity with higher yields.